.container{
    width: 500px;
    height: 300px;
    border: 1px solid #000;
    margin: 10px;
}
.header{
    width: 100%;
    height: 35px;
    background-color:#f5f5f5;
    display: flex;
}
.item{
    text-decoration: none;
    color:#999;
    flex-grow: 1;
    height: 100%;
    background-color: #ccc;
    display: flex;
    justify-content: center;
    align-items: center;
}

.active{
    text-decoration: none;
    color:#fff;
    flex-grow: 1;
    height: 100%;
    background-color:tomato;
    display: flex;
    justify-content: center;
    align-items: center;
}

